Swift is general-purpose ,multi-paradigm, compiled programming language developed by apple for iOS, OS X, watchOS ,tvOS and linux operating system. Swift is built with the LLVM compiler framework included in xcode 6 or later. Swift uses the Objective-C runtime library which allows C ,Objective-C ,C++ and swift Code in single program.

For more detail visit https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/index.html#//apple_ref/doc/uid/TP40014097-CH3-ID0